Mesoscale eddy identification method based on sea surface height and connected domain

Abstract

The invention discloses a mesoscale eddy identification method based on sea surface height and a connected domain, which comprises the following steps of: acquiring sea surface height abnormal data, performing space-time filtering, searching an extreme point of the sea surface height abnormal data as an initial value, and expressing a relationship between sea surface height abnormal data values on surrounding grid points and the extreme point in a 0 / 1 matrix; wherein a point communicating with the extreme point is a point inside the vortex; iteratively searching points in the vortex by properly increasing or decreasing a sea surface height abnormal data threshold value, and when other extreme points communicated with the extreme point exist on the grid boundary, extracting a region contour communicated with the extreme point from the grid in the previous step as a mesoscale vortex boundary; calculating mesoscale vortex characteristics by using vortex internal points; and according to the sea surface temperature abnormal value in the vortex, eigenvalue calculation and recognition of the mesoscale vortex are completed, and preparation is made for subsequent further discussion of the influence of the mesoscale vortex on the atmosphere.

Description

Technical Field

[0001] The present invention relates to the technical field of mesoscale vortex identification, and in particular to a mesoscale vortex identification method based on sea surface height and connected domain. Background Art

[0002] Mesoscale eddies are a typical ocean dynamic phenomenon, with a time scale ranging from tens to hundreds of days and a spatial scale ranging from tens to hundreds of kilometers. Mesoscale eddies can carry the characteristics of water masses from their origin for long-distance transport, and have an important impact on the heat and momentum balance in the ocean and the adjustment of the ecosystem. In addition, mesoscale eddies have a significant impact on the wind field, precipitation, cloud cover, etc. in the upper atmosphere by affecting the momentum exchange of the sea surface, sea level pressure, heat flux at the air-sea interface, and the stability of the air-sea boundary layer.

[0003] Mesoscale vortices can cause changes in sea surface height, temperature, flow field, etc., so these changes can be used to identify them. There are four main types of existing mesoscale vortex identification methods: (1) methods based on physical parameters, the typical representative is the Okubo-Weiss parameter method; (2) methods based on streamline geometry, the typical representative is the angle method; (3) methods based on flow field geometry; (4) methods based on sea surface height anomaly contours. The Okubo-Weiss parameter method uses only one W parameter related to tensile deformation, shear deformation and relative vorticity as a threshold to identify mesoscale vortices. It is simple and has low computational complexity. However, the selection of the W parameter greatly affects the recognition accuracy of the algorithm, and it is difficult to determine a unified optimal threshold for different sea areas. The angle method assumes that a vortex can be defined as the characteristics of instantaneous streamlines that are roughly circular or spiral around its core. First, the instantaneous streamlines are obtained from the velocity field; then the cumulative angle of each streamline segment is calculated, and the vortex is identified by the streamlines with an angle greater than or equal to 2π. The angle method has high recognition accuracy and strong stability. However, the calculation process is complex and requires a lot of calculations. The method based on the geometric characteristics of the flow field identifies the mesoscale vortex by requiring the flow field vector to satisfy several constraints. It has high requirements on the resolution of the flow field and needs careful debugging. The method based on the contour line of sea surface height anomaly identifies the edge of the vortex by finding the outermost closed contour line. The vortex boundary extracted by this type of algorithm is often larger than the actual boundary of the vortex, and it is also unable to identify the situation of mesoscale vortex fusion. Therefore, the identification method of mesoscale vortex still needs to be further improved.

[0004] Since the center of the cyclonic vortex is accompanied by the divergent motion of the water body, and the anticyclonic vortex is accompanied by the convergent motion of the water body in the center of the vortex, in theory, the cyclonic vortex and anticyclonic vortex identified by sea surface height data should correspond to the negative and positive anomalies of the sea surface temperature, respectively. However, studies have found that abnormal vortices exist in many sea areas, namely, cyclonic warm vortices and anticyclonic cold vortices. The reasons for this phenomenon include changes in the vortex radius, such as the increase in the radius of the cyclonic cold vortex, which includes the surrounding warm water, turning the cyclonic cold vortex into a cyclonic warm vortex; the interaction between vortices causes the cold water to be entrained into the anticyclonic warm vortex, thereby turning the anticyclonic warm vortex into an anticyclonic cold vortex. The impact of the vortex on the upper atmosphere is mainly caused by the anomaly of the sea surface temperature caused by the vortex. Therefore, in order to further study the impact of the vortex, it is necessary to distinguish between normal cyclonic cold vortices, anticyclonic warm vortices, and abnormal cyclonic warm vortices and anticyclonic cold vortices for subsequent research. Summary of the invention

[0005] The purpose of the present invention is to provide a mesoscale eddy identification method based on sea surface height and connected domain, which method does not require artificially set thresholds and can identify and distinguish normal and abnormal mesoscale eddies, so as to solve the problems existing in the prior art.

[0006] To achieve the above functions, the present invention designs a mesoscale eddy identification method based on sea surface height and connected domain. For the target sea area, the following steps S1 to S6 are performed to complete the characteristic value calculation and identification of the mesoscale eddy: Step S1: collecting abnormal sea surface height data of the target sea area, filtering the abnormal sea surface height data, and performing grid division, finding the extreme value points of the abnormal sea surface height data within a preset range around each grid point, marking the positions thereof, and taking the positions corresponding to the extreme value points of the abnormal sea surface height data as the potential centers of the mesoscale vortices; Step S2: taking the extreme value of the sea surface height anomaly data as the initial threshold, comparing the size relationship between the sea surface height anomaly data within a preset range around the extreme value point and the extreme value, and finding a point connected to the position of the extreme value point of the sea surface height anomaly data according to the size relationship as the point inside the mesoscale vortex; Step S3: extracting the contour of the region connected to the extreme point from the range in step S2 as the boundary of the mesoscale vortex; Step S4: based on the points inside the mesoscale vortex and the potential center of the mesoscale vortex, the centroid of the mesoscale vortex is calculated as the center of the mesoscale vortex; Step S5: calculating the characteristic value of the mesoscale vortex based on the points inside the mesoscale vortex and the boundary of the mesoscale vortex; Step S6: Based on the center of the mesoscale vortex and the characteristic value of the mesoscale vortex, and according to the abnormal value of the sea surface temperature inside the mesoscale vortex, whether the mesoscale vortex is normal or not is judged and marked.

[0007] Beneficial effects: Compared with the prior art, the advantages of the present invention include: The method designed by the present invention is based on the abnormal sea surface height data to identify the mesoscale vortex, without artificially set parameters. This method can avoid the error introduced by taking the partial derivative of the abnormal sea surface height data, and can also avoid the error caused by artificially setting the threshold. It is possible to effectively obtain the points inside the mesoscale vortex, determine its boundaries, and then perform statistical analysis on the vortex characteristics. Combined with the sea surface temperature data, it is possible to further distinguish between normal cyclonic cold vortices, anticyclonic warm vortices and abnormal cyclonic warm vortices, anticyclonic cold vortices, thereby determining the spatiotemporal changes of mesoscale vortices in each sea area, and preparing for further exploration of the impact of mesoscale vortices on the atmosphere. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is a flow chart of a mesoscale eddy identification method based on sea surface height and connected domain provided according to an embodiment of the present invention; Figure 2 is a schematic diagram of sea surface height extreme value extraction according to an embodiment of the present invention; Figure 3 is a schematic diagram of a vortex boundary and a central extreme point provided according to an embodiment of the present invention; Figure 4 is a spatial distribution diagram of the annual average number of vortices, vortex radius, vortex kinetic energy and vorticity provided according to an embodiment of the present invention; Figure 5 It is a schematic diagram of a normal cyclonic cold vortex, an anticyclonic warm vortex, and an abnormal cyclonic warm vortex, and an anticyclonic cold vortex provided according to an embodiment of the present invention; Figure 6 It is a schematic diagram of the anomaly in sea surface height, the sea surface flow field and the anomaly in sea surface temperature corresponding to the normal cyclonic cold vortex, anticyclonic warm vortex and the abnormal cyclonic warm vortex and anticyclonic cold vortex provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0009] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0010] The embodiment of the present invention provides a mesoscale eddy identification method based on sea surface height and connected domain. For a target sea area, the following steps S1 to S6 are executed to complete the characteristic value calculation and identification of the mesoscale eddy: Step S1: Collect the sea level anomaly (SLA) data of the target sea area, filter the sea level anomaly data, and perform grid division, find the extreme value points of the sea level anomaly data within a preset range around each grid point, mark their locations, and use the positions corresponding to the extreme value points of the sea level anomaly data as the potential centers of the mesoscale vortices; Taking the identification of cyclonic vortices as an example, a flow chart of a mesoscale vortex identification method based on sea surface height and connected domain provided by an embodiment of the present invention is shown in FIG. Figure 1 ; The specific steps of step S1 are as follows: Step S1.1: Collect sea surface height anomaly data with a spatial resolution of 0.25°; use the local weighted regression method to perform spatial high-pass filtering of the sea surface height anomaly data at 20° longitude × 10° latitude to eliminate the influence of large-scale processes; and use the Fourier filter to perform temporal low-pass filtering at a scale of 15 days to eliminate the influence of weather-scale events; Step S1.2: The sea surface height anomaly data is gridded. Taking each grid point as the center, find the extreme points of the sea surface height anomaly data in the surrounding 5×5 grid points, including positive maximum points and negative minimum points, and mark the location of the extreme point as 1, and the location of the non-extreme point as 0.

[0011] like Figure 2 The figure shows the sea surface height anomaly data and the corresponding extreme values ​​after spatial high-pass filtering in the target sea area on January 5, 2000. These extreme values ​​will be used as the starting values ​​for finding the internal points of the mesoscale vortex.

[0012] Step S2: taking the extreme value of the sea surface height anomaly data as the initial threshold, comparing the size relationship between the sea surface height anomaly data within a preset range around the extreme value point and the extreme value, and finding a point connected to the position of the extreme value point of the sea surface height anomaly data according to the size relationship as the point inside the mesoscale vortex; The specific steps of step S2 are as follows: Step S2.1: If the cyclone vortex is to be identified, for the minimum value point of the sea surface height anomaly data at any time step, the minimum value point is taken as the central extreme value point, and the size relationship between the sea surface height anomaly data on the grid point and the minimum value point is determined in the 11×11 grids above, below, left and right of the minimum value point. If the sea surface height anomaly data on the grid point is less than the minimum value, it is marked as 1, otherwise it is marked as 0; Step S2.2: If the anticyclonic vortex is to be identified, for the maximum point of the sea surface height anomaly data at any time step, the maximum point is taken as the central extreme point, and the size relationship between the sea surface height anomaly data on the grid point and the maximum point is determined in the 11×11 grids above, below, left and right of the maximum point. If the sea surface height anomaly data on the grid point is greater than the maximum value, it is marked as 1, otherwise it is marked as 0; Step S2.3: According to steps S2.1 and S2.2, a two-dimensional 0 / 1 matrix is ​​obtained, and corresponding points that are also marked as 1 and adjacent to the location of the central extreme point under the eight-connectivity condition (horizontally, vertically or diagonally) are found as points inside the mesoscale vortex.

[0013] In step S2, if there are points connected to the central extreme point on the boundary of the 11×11 grids, expand one layer of grids outward and continue to search for points connected to the central extreme point in the 13×13 grids; if there are still points connected to the central extreme point on the grid boundary, continue to expand one layer of grids outward and repeat step S2.3.

[0014] If there is no point connected to the central extreme point on the boundary of the grid, if the central extreme point is a minimum value, the central extreme point is increased by a preset value, and if the central extreme point is a maximum value, the central extreme point is decreased by a preset value, and the increased or decreased central extreme point is used as the initial threshold to repeat the comparison within the current grid range; this is repeated iteratively until another extreme point connected to the central extreme point is found on the boundary of the search grid. In one embodiment, if there is no point connected to the central extreme point on the boundary of the grid, the value of the central extreme point is increased or decreased by , N is the number of iterations, N =0, the corresponding grid range is 11×11.

[0015] In fact, step S2 takes the central extreme point as the initial value, and gradually searches outward for the closed contour line of the sea level height anomaly data with the largest range. The points connected to the central extreme point within this contour line are the points inside the vortex.

[0016] Step S3: extracting the contour of the region connected to the extreme point from the range in step S2 as the boundary of the mesoscale vortex; The specific method of step S3 is as follows: When another extreme point connected to the central extreme point is found on the boundary of the grid, and there are at least 9 points connected to the central extreme point inside the mesoscale vortex, and the land points on the boundary of the mesoscale vortex are less than 30%, then we take a step back and extract the contour of the area connected to the central extreme point from the grid range in the previous layer to determine the boundary of the mesoscale vortex. In order to obtain a compact vortex, when the latitude is greater than 25º, the maximum distance between any two points in the mesoscale vortex is required to be no more than 400km, and when the latitude is below 25º, the maximum distance between any two points in the mesoscale vortex is required to be no more than 1200km.

[0017] like Figure 3 The figure shows the cyclonic vortex and anticyclonic vortex in the target sea area on January 5, 2000. This method of identifying vortices effectively avoids the fusion of vortices, each vortex has only one extreme value, and the resulting vortex shape is reasonable.

[0018] Step S4: based on the points inside the mesoscale vortex and the potential center of the mesoscale vortex, the centroid of the mesoscale vortex is calculated as the center of the mesoscale vortex; The distances between all points inside the mesoscale eddy and the extreme points of the sea surface height anomaly data are calculated respectively, and the weighted average is performed to obtain the centroid of the mesoscale eddy, which is taken as the center of the mesoscale eddy.

[0019] Step S5: calculating the characteristic value of the mesoscale vortex based on the points inside the mesoscale vortex and the boundary of the mesoscale vortex; The specific steps of step S5 are as follows: Step S5.1: taking the average difference between the extreme point of the sea surface height anomaly data and the boundary of the mesoscale eddy as the amplitude of the mesoscale eddy; Step S5.2: Based on the known geostrophic relationship, the geostrophic velocity anomalies of the internal and edge points of the mesoscale vortex are calculated as follows: ; ; in, u , v are the latitudinal and longitudinal geostrophic velocity anomalies, g is the acceleration due to gravity, f is the Coriolis parameter, SLA is the sea surface height anomaly data, , are the latitudinal and longitudinal distances between adjacent points respectively; Step S5.3: Calculate the average eddy kinetic energy of the mesoscale vortex using the average value of the eddy kinetic energy of each point in the mesoscale vortex, as shown in the following formula: ; in, EKE represents the mean eddy kinetic energy; Step S5.4: Calculate the average vorticity of the mesoscale vortex using the average value of the vorticity of each point in the mesoscale vortex, as shown in the following formula: ; in, curl represents the mean vorticity; Step S5.5: Calculate the radius of the mesoscale vortex using the radius of a circle that is equal to the area occupied by the mesoscale vortex, as shown in the following formula: ; in, R is the radius of the mesoscale vortex, S is the area of ​​the mesoscale vortex; Step S5.6: Calculate the shear deformation of the mesoscale vortex, as follows: ; in, shear represents the shear deformation of the mesoscale vortex; Step S5.7: Calculate the stretching deformation of the mesoscale vortex, as follows: ; in, stretch represents the stretching deformation of the mesoscale vortex; Step S5.8: Calculate the average deformation of the mesoscale vortex, as follows: ; in, D represents the average deformation of the mesoscale eddy.

[0020] Step S6: Based on the center of the mesoscale eddy and the characteristic value of the mesoscale eddy, and according to the Sea Surface Temperature Anomaly (SSTA) value inside the mesoscale eddy, whether the mesoscale eddy is normal or not is judged and marked.

[0021] Figure 4 The spatial distribution of the annual average number of vortices, vortex radius, vortex kinetic energy and vorticity is shown; Figure 4 (a)- Figure 4 (d) The average number, radius, vortex kinetic energy and vorticity of vortices from 2000 to 2009. The distribution of vortex radius is similar to that of Rossby deformation radius, with large radius at low latitudes and smaller average radius at higher latitudes. The average kinetic energy and average vorticity of vortices have high value areas in the southwest, indicating that the vortex activity in this area is strong.

[0022] The specific steps of step S6 are as follows: Step S6.1: Use the local weighted regression method to perform spatial high-pass filtering of the sea surface temperature at 3° longitude × 3° latitude, and use the Fourier filter to perform low-pass filtering over 15 days to obtain the sea surface temperature anomaly value; Step S6.2: using the center of the mesoscale vortex identified in step S4 and the radius of the mesoscale vortex calculated in step S5, calculate the average sea surface temperature anomaly within a radius of the center of the mesoscale vortex; Step S6.3: If the average sea surface temperature anomaly value corresponding to the minimum value of the sea surface height anomaly data is negative, the mesoscale vortex is judged to be a normal cyclonic cold vortex; if the average sea surface temperature anomaly value corresponding to the maximum value of the sea surface height anomaly data is positive, the mesoscale vortex is judged to be a normal anticyclonic warm vortex, and the normal mesoscale vortex is marked as 1; If the average sea surface temperature anomaly value corresponding to the minimum value of the sea surface height anomaly data is positive, the mesoscale vortex is judged to be an abnormal cyclonic warm vortex; if the average sea surface temperature anomaly value corresponding to the maximum value of the sea surface height anomaly data is negative, the mesoscale vortex is judged to be an abnormal anticyclonic cold vortex, and the abnormal mesoscale vortex is marked as 0.

[0023] Figure 5 It shows the normal cyclonic cold vortex, anticyclonic warm vortex, and abnormal cyclonic warm vortex and anticyclonic cold vortex; Figure 5 (a)- Figure 5 (d) They are cyclonic cold vortex, cyclonic warm vortex, anticyclonic warm vortex and anticyclonic cold vortex. A normal cyclonic cold vortex is displayed as a closed contour line of sea surface height anomaly data on the sea surface height anomaly data image, which surrounds the minimum value of the sea surface height anomaly data, and corresponds to the average negative average sea surface temperature anomaly value inside the vortex on the sea surface temperature anomaly image; a normal anticyclonic warm vortex is displayed as a closed contour line of sea surface height anomaly data on the sea surface height anomaly data image, which surrounds the maximum value of the sea surface height anomaly data, and corresponds to the average positive average sea surface temperature anomaly value inside the vortex on the sea surface temperature anomaly image; an abnormal cyclonic warm vortex is displayed as a closed contour line of sea surface height anomaly data on the sea surface height anomaly data image, which surrounds the minimum value of the sea surface height anomaly data, and corresponds to the average positive average sea surface temperature anomaly value inside the vortex on the sea surface temperature anomaly image; an abnormal anticyclonic cold vortex is displayed as a closed contour line of sea surface height anomaly data on the sea surface height anomaly data image, which surrounds the maximum value of the sea surface height anomaly data, and corresponds to the average negative average sea surface temperature anomaly value inside the vortex on the sea surface temperature anomaly image.

[0024] Figure 6 It shows the sea surface height anomaly, sea surface flow field and sea surface temperature anomaly corresponding to the normal cyclonic cold vortex, anticyclonic warm vortex and abnormal cyclonic warm vortex and anticyclonic cold vortex. Figure 6 (a)- Figure 6 (d) The sea surface height anomaly, sea surface flow field and sea surface temperature anomaly corresponding to the cyclonic cold vortex, cyclonic warm vortex, anticyclonic warm vortex and anticyclonic cold vortex are shown in order; by using steps S1 to S6 to statistically analyze the mesoscale vortices in the target sea area from 2000 to 2009, it is found that there are 10,137 cyclonic vortices in 10 years, of which 7,038 (69.43%) are cold vortices and 3,099 (30.57%) are warm vortices; there are 9,253 anticyclonic vortices, of which 6,051 (65.40%) are warm vortices and 3,202 (34.6%) are cold vortices, and most of the vortices are normal types of vortices. Synthetic analysis is performed on the cyclonic cold vortex, cyclonic warm vortex, anticyclonic warm vortex and anticyclonic cold vortex respectively, and it is found that from the sea surface height anomaly data, the intensity of the four vortices is about 5 cm. Cyclonic vortices can cause counterclockwise rotation of the sea surface flow field anomalies, while anticyclonic vortices can cause clockwise rotation of the sea surface flow field anomalies. It can be seen that the changes in the sea surface flow field are mainly determined by the changes in the sea surface height. From the perspective of sea surface temperature anomalies, cyclonic cold vortices correspond to cold anomalies in the vortex center, which can reach -0.16°C, while cyclonic warm vortices correspond to warm anomalies in the vortex center, with a maximum value of 0.07°C, which is weaker than the normal cyclonic cold vortex intensity; anticyclonic warm vortices correspond to warm anomalies in the vortex center, which can reach 0.09°C, while anticyclonic cold vortices correspond to cold anomalies in the vortex center, which can reach -0.07°C.

[0025] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in this field without departing from the purpose of the present invention.

Claims

1. A mesoscale eddy identification method based on sea surface height and connected domain, characterized in that: For the target sea area, the following steps S1 to S6 are executed to complete the calculation and identification of the eigenvalues ​​of the mesoscale eddy: Step S1: collecting abnormal sea surface height data of the target sea area, filtering the abnormal sea surface height data, and performing grid division, finding the extreme value points of the abnormal sea surface height data within a preset range around each grid point, marking the positions thereof, and taking the positions corresponding to the extreme value points of the abnormal sea surface height data as the potential centers of the mesoscale vortices; Step S2: taking the extreme value of the sea surface height anomaly data as the initial threshold, comparing the size relationship between the sea surface height anomaly data within a preset range around the extreme value point and the extreme value, and finding a point connected to the position of the extreme value point of the sea surface height anomaly data according to the size relationship as the point inside the mesoscale vortex; Step S3: extracting the contour of the area connected to the extreme point from the range in step S2 as the boundary of the mesoscale vortex; Step S4: based on the points inside the mesoscale vortex and the potential center of the mesoscale vortex, the centroid of the mesoscale vortex is calculated as the center of the mesoscale vortex; Step S5: calculating the characteristic value of the mesoscale vortex based on the points inside the mesoscale vortex and the boundary of the mesoscale vortex; Step S6: Based on the center of the mesoscale vortex and the characteristic value of the mesoscale vortex, and according to the abnormal value of the sea surface temperature inside the mesoscale vortex, whether the mesoscale vortex is normal or not is judged and marked.

2. A mesoscale eddy identification method based on sea surface height and connected domain according to claim 1, characterized in that: The specific steps of step S1 are as follows: Step S1.1: Collect sea surface height anomaly data with a spatial resolution of 0.25°; use the local weighted regression method to perform spatial high-pass filtering of the sea surface height anomaly data at 20° longitude × 10° latitude; and use the Fourier filter to perform temporal low-pass filtering with a scale of 15 days; Step S1.2: The sea surface height anomaly data is gridded. Taking each grid point as the center, find the extreme points of the sea surface height anomaly data in the surrounding 5×5 grid points, including positive maximum points and negative minimum points, and mark the location of the extreme point as 1, and the location of the non-extreme point as 0.

3. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 1, characterized in that: The specific steps of step S2 are as follows: Step S2.1: If the cyclone vortex is to be identified, for the minimum value point of the sea surface height anomaly data at any time step, the minimum value point is taken as the central extreme value point, and the size relationship between the sea surface height anomaly data on the grid point and the minimum value point is determined in the 11×11 grids above, below, left and right of the minimum value point. If the sea surface height anomaly data on the grid point is less than the minimum value, it is marked as 1, otherwise it is marked as 0; Step S2.2: If the anticyclonic vortex is to be identified, for the maximum point of the sea surface height anomaly data at any time step, the maximum point is taken as the central extreme point, and the size relationship between the sea surface height anomaly data on the grid point and the maximum point is determined in the 11×11 grids above, below, left and right of the maximum point. If the sea surface height anomaly data on the grid point is greater than the maximum value, it is marked as 1, otherwise it is marked as 0; Step S2.3: According to step S2.1-step S2.2, a two-dimensional 0 / 1 matrix is ​​obtained, and corresponding points that are also marked as 1 and adjacent to the location of the central extreme point under the eight-connectivity condition are found as points inside the mesoscale vortex; the eight-connectivity condition refers to connectivity in the horizontal, vertical or diagonal direction.

4. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 3, characterized in that: In step S2, if there are points connected to the central extreme point on the boundaries of the 11×11 grids, then expand one layer of grids outward, and continue to search for points connected to the central extreme point in the 13×13 grids; if there are still points connected to the central extreme point on the grid boundary, then continue to expand one layer of grids outward, and repeat step S2.3; if there are no points connected to the central extreme point on the grid boundary, if the central extreme point is a minimum value, then increase the central extreme point by a preset value; if the central extreme point is a maximum value, then decrease the central extreme point by a preset value, and use the increased or decreased central extreme point as the initial threshold to repeat the comparison within the current grid range; and repeat in this way until there is another extreme point connected to the central extreme point on the search grid boundary.

5. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 4, characterized in that: In step S2, if there is no point on the boundary of the grid that is connected to the central extreme point, the value of the central extreme point is increased or decreased by , N is the number of iterations. When N=0, the corresponding grid range is 11×11.

6. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 4, characterized in that: The specific method of step S3 is as follows: When another extreme point connected to the central extreme point is found on the boundary of the grid, and there are at least 9 points connected to the central extreme point inside the mesoscale vortex, and the percentage of land points on the boundary of the mesoscale vortex is less than 30%, then we take a step back and extract the outline of the area connected to the central extreme point from the range of the grid in the previous layer to determine it as the boundary of the mesoscale vortex.

7. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 6, characterized in that: In step S3, when the latitude is greater than 25°, the maximum distance between any two points in the mesoscale vortex is required to be no more than 400 km, and when the latitude is below 25°, the maximum distance between any two points in the mesoscale vortex is required to be no more than 1200 km.

8. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 1, characterized in that: In step S4, the distances between all points inside the mesoscale vortex and the extreme points of the sea surface height anomaly data are calculated respectively, and weighted average is performed to obtain the centroid of the mesoscale vortex as the center of the mesoscale vortex.

9. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 1, characterized in that: The specific steps of step S5 are as follows: Step S5.1: taking the average difference between the extreme point of the sea surface height anomaly data and the boundary of the mesoscale eddy as the amplitude of the mesoscale eddy; Step S5.2: Calculate the geostrophic velocity anomalies at the inner and edge points of the mesoscale vortex, as follows: ； ； in, u , v are the latitudinal and longitudinal geostrophic velocity anomalies, g is the acceleration due to gravity, f is the Coriolis parameter, SLA is the sea surface height anomaly data, , are the latitudinal and longitudinal distances between adjacent points respectively; Step S5.3: Calculate the average eddy kinetic energy of the mesoscale eddy, as follows: ； in, EKE represents the mean eddy kinetic energy; Step S5.4: Calculate the average vorticity of the mesoscale eddy, as follows: ； in, curl represents the mean vorticity; Step S5.5: Calculate the radius of the mesoscale vortex, as follows: ； in, R is the radius of the mesoscale vortex, S is the area of ​​the mesoscale vortex; Step S5.6: Calculate the shear deformation of the mesoscale vortex, as follows: ； in, shear represents the shear deformation of the mesoscale vortex; Step S5.7: Calculate the stretching deformation of the mesoscale vortex, as follows: ； in, stretch represents the stretching deformation of the mesoscale vortex; Step S5.8: Calculate the average deformation of the mesoscale vortex, as follows: ； in, D represents the average deformation of the mesoscale eddy.

10. The method for identifying mesoscale eddies based on sea surface height and connected domain according to claim 1, characterized in that: The specific steps of step S6 are as follows: Step S6.1: Use the local weighted regression method to perform spatial high-pass filtering of the sea surface temperature at 3° longitude × 3° latitude, and use the Fourier filter to perform low-pass filtering over 15 days to obtain the sea surface temperature anomaly value; Step S6.2: using the center of the mesoscale vortex identified in step S4 and the radius of the mesoscale vortex calculated in step S5, calculate the average sea surface temperature anomaly within a radius of the center of the mesoscale vortex; Step S6.3: If the average sea surface temperature anomaly value corresponding to the minimum value of the sea surface height anomaly data is negative, the mesoscale vortex is judged to be a normal cyclonic cold vortex; if the average sea surface temperature anomaly value corresponding to the maximum value of the sea surface height anomaly data is positive, the mesoscale vortex is judged to be a normal anticyclonic warm vortex, and the normal mesoscale vortex is marked as 1; If the average sea surface temperature anomaly value corresponding to the minimum value of the sea surface height anomaly data is positive, the mesoscale vortex is judged to be an abnormal cyclonic warm vortex; if the average sea surface temperature anomaly value corresponding to the maximum value of the sea surface height anomaly data is negative, the mesoscale vortex is judged to be an abnormal anticyclonic cold vortex, and the abnormal mesoscale vortex is marked as 0.

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